Polypropylene-polybutylene laminated packaging film with improved tear strength

Abstract

A packaging film composition having an improved tear strength comprising a core, which is preferably polybutylene homopolymer or copolymer or a blend of polybutylene with another compatible polymer, said core being coated on one or both sides with a polypropylene homopolymer or copolymer optionally blended with a minor amount of a high melt index polybutylene.

What is claimed is: 
     
       1. A multiple-layer, heat-sealable laminated film comprising: (a) a core layer formed from a member of the group consisting of butene-1 homopolymers and copolymers of butene-1 with ethylene wherein the ethylene content is 0.25% to 15% by weight; and   (b) on both sides of said core, an outer layer which comprises about 90% by weight to about 99% by weight of a homopolymer or copolymer of propylene and about 1% by weight to about 10% by weight of a high melt index, isotactic polybutylene with a melt index in the range of from about 100 to about 1000.   
     
     
       2. The laminated film of claim 1 wherein said high melt index polybutylene has a melt index in the range of about 150 to about 225. 
     
     
       3. The laminated film of claim 1 wherein said high melt index polybutylene is selected from the group consisting of: butene-1 homopolymers and butene-1 copolymers having 1-30 mole% of an alpha olefin having from 2-8 carbon atoms. 
     
     
       4. The laminated film of claim 1, wherein said propylene homopolymer or copolymer is selected from the group consisting of: propylene homopolymers and propylene copolymers having 1-30 mole% of an alpha olefin having from 2-8 carbon atoms. 
     
     
       5. The laminated film of claim 1, wherein said outer layer comprises about 93% to about 97% by weight of said propylene polymer and about 3% to about 7% by weight of said high melt index polybutylene. 
     
     
       6. The laminated film of claim 1 wherein said outer layer is from about 0.3 mils to about 0.6 mils thick and the total film thickness is between 0.9 and 2.0 mils. 
     
     
       7. The laminated film of claim 1 wherein the film is oriented by stretching in two directions substantially at right angles to each other. 
     
     
       8. The laminated film of claim 1 wherein the film is formed by coextrusion.